This invention pertains to valves and particularly to a dual valve of the annular type which may be included in a string of well tools or well tubing and operated by ambient pressures to control flow through flow ports in the valve housing wall.
In a well completed for production using pumpdown or through flow line techniques and tools, the tool string pumped down the production tubing to open the tubing to flow from a producing formation usually includes a ball type check valve. The primary function of the ball type check valve, which is old and well known, is to protect the producing formation from back pressures which may occur while circulating fluids through the pumpdown system or when system pressure is increased to cause positive actuation of servicing tools during service operations. Flow back into producing formations, caused by pressures at the formation producing interval face higher than formation pressure, can be very detrimental to the producing ability of a formation. If the formation is permanently damaged by flow into and cannot be repaired by expensive workover procedures, cumulative production from the formation may be definitely limited and the life of the well shortened, resulting in great economic loss.
Ordinary ball-type check valves previously utilized in well tool strings in production tubing inherently limit well production flow and only function in a formation protecting capacity to prevent reverse flow to kill wells or pump into formations.
One type of annular valve operated by pressure is disclosed in U.S. Pat. No. 3,403,694 to Brown.